1. Field of the Invention
The present invention generally relates to plated through-holes for an electronic component assembly and to an associated method for making the through-holes which eliminates the need to use discrete wires and printed flexes as connectors between circuits on the electronic component assembly.
2. State of the Art
A circuit element situated on one printed wiring board located on one side of an electronic component assembly is, at times, required to be connected to another circuit element located on another printed wiring board located on the opposite side of the electronic circuit assembly. Connections can be run from one side of the electronic component assembly to the other through the use of discrete wires or printed flexes which are connected to the circuit elements. This is done after the electronic component assembly has been assembled or after each component is attached to the printed wiring boards. As a result, however, more production time is required to connect the discrete wires and printed flexes between wiring boards on opposite sides of an electronic component assembly. Furthermore, the use of discrete wires and printed flexes after the manufacturing of the electronic component assembly requires a high degree of precision labor which is more expensive and has a higher incidence of errors occurring during manufacture.
The use of through-holes has been employed to provide communication from one layer of a printed wiring board of an electronic component assembly to another layer. For example, U.S. Pat. No. 3,739,469 (Dougherty, Jr.) describes a method for fabricating multi-layer circuit boards with vias in the internal layers that are concentric with plated through-holes. However, the internal vias are xe2x80x9cpluggedxe2x80x9d with a dielectric pre-peg used during a lamination phase of the fabrication process. That is, excess dielectric material which is a by-product of the lamination process can result in an insufficient amount dielectric material filling the through-hole. This can result in improper plating of the through-hole and incorrect circuit operation.
In addition, due to the internal structure of electronic component assemblies, properly placing through holes is difficult. Heat sinks located at the core of the electronic component assembly present problems when forming the through holes.
U.S. Pat. No. 5,562,971 (Tsuru et al.) discloses the placement of through-holes in a multi-layer printing board. The through holes are drilled after the formation of the circuit board and insulating layers are laminated by heating under pressure. A conductive layer is then placed over the drilled hole. In this case, there is no heat sink at the core of the electronic component assembly.
Electrical circuits contained in the printed wiring boards have a common xe2x80x9ccircuit ground potentialxe2x80x9d while the chassis, to which electronic component assemblies are connected, includes a separate xe2x80x9cchassis ground potentialxe2x80x9d . The separate ground circuits are maintained to avoid electrical problems. For example, if the different ground elements of the circuit and the chassis, to which an electronic component assembly is connected, are brought into contact, a ground loop can form between the printed wiring boards which raises the potential of the circuit ground above zero volts and renders the electrical circuits susceptible to noise. The proper operation of circuits which use discrete logic levels can be affected when noise distorts the circuit ground to a value greater than zero volts.
Known methods of connecting one printed wiring board to another through the use of connectors are labor intensive and require a high degree of precision to avoid short circuits. Accordingly, an efficient, cost-effective technique to run a connection from one side of an electronic component assembly to the other is needed.
The present invention is directed to an electronic component assembly and an allocated method of manufacture which can be efficiently implemented and which reduces the amount of work required to create a plated through-hole for connecting one circuit to another circuit in an electronic component assembly. Exemplary embodiments ensure that during electronic component assembly fabrication, at least a portion of an inner core of the electronic component assembly""s heat sink assembly is replaced with a dielectric xe2x80x9czone.xe2x80x9d When the electronic component assembly is manufactured, connections from one circuit on one side of the electronic component assembly to another circuit on the other side of the electronic component assembly are achieved using plated through-holes. As such, circuit boards can be electrically connected on opposite sides of the electronic component assembly without having to perform the labor intensive connection of circuits through the use of discrete wires or printed flexes. The plated through holes are made through dielectric zones selectively placed into the inner core of the electronic component assembly.
Generally speaking, exemplary embodiments relate to an electronic component assembly which comprises at least first and second electrical circuits and a heat sink assembly connected to the first and second electrical circuits, the heat sink assembly including an inner core having at least a first portion made of a dielectric material having a through-hole from the first electrical circuit to the second electrical circuit, and a second portion made of a material that is different from the dielectric material, wherein the first portion is one of co-cured and bonded with the second portion.
In another exemplary embodiment of the present invention, a method for producing a heat sink assembly is disclosed which comprises the steps of: providing an inner core made of a heat sink material, forming a segment of the heat sink material with a first dielectric segment wherein a through-hole is to be established from a first electrical circuit to a second electrical circuit, placing a second dielectric around the inner core, selectively plating the second dielectric with a first electrically conductive foil and plating a conductive material on the first electrically conductive foil, placing first and second electrical circuits on the second dielectric and on opposite sides of the inner core, and making a through hole from the first electrical circuit through the first dielectric segment of the inner core to the second electrical circuit.